4. How to improve ventilation
If you identify an area that needs improved ventilation to reduce the risk of spreading COVID-19, you should decide if it's safe for people to continue to use it while you are making the improvements.
Practical ways to improve your ventilation include:
- increasing natural ventilation by opening doors, windows and vents
- ensuring any mechanical ventilation system is set to maximise fresh air and minimise air recirculation
You may need a combination of natural ventilation and mechanical ventilation.
How to improve natural ventilation
You can improve natural ventilation by fully or partly opening windows, air vents and doors. Don't prop fire doors open.
Buildings are usually designed to provide adequate ventilation. You should be able to open any windows or vents that let in fresh air. If they cannot be opened, ventilation in that area will be less effective.
Don't close doors or windows completely when people are in a naturally ventilated area. This can result in very low levels of ventilation.
Cooler, windier weather increases natural ventilation through openings. This means you don't need to open windows and doors so wide. See if you can open any trickle vents in your workplace.
We have more advice on balancing ventilation with keeping people warm at work.
Airing rooms (purging)
Airing rooms as frequently as you can improves ventilation. Opening all the doors and windows as fully as possible maximises ventilation in a room. You can do this when people leave for a break and even 10 minutes an hour can help reduce the risk from virus in the air, depending on the size of the room.
How to improve mechanical ventilation
Mechanical ventilation brings fresh air into a building from outside.
You should speak to the people who manage the day-to-day operations of your workplace's mechanical ventilation systems to:
- understand how they operate
- make sure they're supplying fresh air into an area and how much
- make sure they're maintained in line with manufacturers' instructions
Don't lower mechanical ventilation rates if the number of people in an area reduces temporarily.
You should base ventilation rates on the maximum 'normal' occupancy of an area.
You may need a ventilation engineer to check your system is providing adequate ventilation and service the system to ensure it is working properly.
Maximising fresh air
Mechanical systems will provide adequate ventilation if they are set to maximise fresh air and minimise recirculation.
If your system draws in fresh air, it can continue to operate. You need to know how much fresh air it draws in and if this provides adequate ventilation.
You may need to increase the rate or supplement it with natural ventilation (for example, by opening doors, windows or air vents) where possible.
You could also consider extending the operating times of mechanical ventilation systems to before and after people use work areas.
Recirculating air will not improve ventilation
Don't rely on recirculating air, this will only move air around and could carry COVID-19 through a space if someone is infected.
Recirculation units for heating and cooling that do not draw in a supply of fresh air can remain in operation as long as there is a supply of outdoor air. This could mean improving natural ventilation by leaving windows and doors open.
Recirculation units (including air conditioning) can mask poor ventilation as they only make an area feel more comfortable.
If your ventilation is still poor
If your ventilation is still inadequate (for example if CO2 readings remain above recommended levels or the room continues to feel stuffy) you should consider:
- changing how workspaces are used, for example restricting the length of time people spend in them or the number of people using them at a single time
- installing a mechanical ventilation system (upon advice from a ventilation engineer), if there is no mechanical ventilation already or if the existing system does not provide fresh air
Air cleaning or filtration is not a substitute for good ventilation, but where poor ventilation cannot be improved, these systems can reduce airborne coronavirus in a space.
Find out more
Our examples of improving ventilation to reduce transmission provide further advice on practical steps you can take.
We review and update this page regularly to reflect any changes in guidance.
Page last reviewed: 19 January 2022
Next review due: 30 January 2022